Background The incidence of severe postoperative pain after shoulder surgery is 30% to 70%.The postoperative pain should be relieved for early rehabilitation and recovery. Patient-controlled analgesia (PCA) with opiate therapy may control some of the postoperative pain, but it has several side effects such as nausea, vomiting, and dizziness, which can prevent early discharge. Conversely, there are several regional blocks to control postoperative pain. Interscalene brachial plexus block (ISB) is known as one of the most effective regional blocks for shoulder surgery, but it has relatively short duration of effect.